1. Field of the Invention
The present invention relates to an inkjet head and a method of cleaning the inkjet head, and more particularly to cleaning the inkjet head used in the inkjet recording apparatus so that fouling such as ink adhering around the inkjet head can be removed in a non-contact way without using a blade.
2. Description of the Related Art
An inkjet printer is known such that recording is performed by supplying ink to an inkjet head and discharging the ink in the form of ink droplets from nozzles of the inkjet head toward recording paper. Since an inkjet printer carries out recording by expelling (or discharging) ink from nozzles, a portion of the expelled ink is dispersed in the form of a fine mist. This kind of ink mist, dust from the recording paper (i.e. small shards of paper), or other dirt adheres around the nozzles. If the vicinity of the nozzles becomes soiled to the ink mist, the paper dust, or the other dirt, the flight direction of the ink droplets discharged from the nozzles might change and the achievement of high quality printing might be impossible.
In order to prevent this problem, a head cleaning method in the related art such that the surface of the nozzles is wiped with a blade (or wiper) made from a flexible material such as rubber to remove fouling around the nozzles is commonly used. However, in this method, since the blade slides on and wipes off the nozzle surface, a drawback arises in that it may cause scratches in the nozzle surface or deterioration of the surface processing such as liquid resistance treatment, and stable discharge of the ink over a long period of time might become impossible. Therefore, in place of cleaning method using the blade, various non-contact methods of collecting fouling such as ink around the inkjet head into the interior portion of the nozzles have been proposed.
Japanese Patent Application Publication No. 3-293140 discloses a method of cleaning the peripheral region of a discharge port. According to this patent document, by controlling the energy for discharging ink from the discharge port as ink droplets, column-shaped ink is created, which is not an ink droplet discharged from the discharge port. When ink is refilled into the discharge port, the discharged column-shaped ink spreads about the periphery of the discharge port and combines with the fouling surrounding the discharge port. Then it is suctioned inside the discharge port to collect the fouling.
However, the method disclosed in Japanese Patent Application Publication No. 3-293140 implies a problem in that, since an incomplete pulse or drive waveform resulting in incomplete discharge is supplied in order to create the column-shaped ink for collecting the fouling which is not discharged, the state of the ink droplets is extremely unstable. In some cases, it might be impossible to collect the ink droplets depending on ambient temperature, etc.
Japanese Patent Application Publication No. 3-193354 discloses a method of cleaning the surface of a nozzle. According to this patent document, the viscosity of the ink increases after the nozzle surface of the inkjet head is sealed with a cap preventing the ink in the discharge port from evaporating on standby. If the ink is expelled from the discharge port prior to recording, a portion of the ink might adhere to the nozzle surface. In this case, by controlling the pressure inside the discharge port to become lower than the pressure outside the discharge port, the ink adhered to the nozzle surface is suctioned inside the discharge port to collect the ink.
However, the method described in Japanese Patent Application Publication No. 3-193354 assumes that the adhered ink drops are connected to ink meniscus (i.e. ink boundary) inside the nozzle. This relates to collection of fouling in the case that the ink adheres to the nozzle surface due to capping, but is not applicable to a case that the fouling is separated from the ink meniscus inside the nozzle.